Ross, 48, was in uniform and working on the CTA detail at the Grand Avenue Blue Line stop around 9 a.m. when he suffered the heart attack. Police News affairs said. He was taken to Northwestern Memorial Hospital, where he died, police said.

Ross had been on the force for 25 years and received 17 awards from the department during his career, police said.

"On behalf of the entire Department, I offer my sincere condolences to Officer Ross' family, friends and colleagues," Police Superintendent Garry McCarthy said in the statement. "We will keep them in our thoughts and prayers during this difficult time."

The officer was taken to Northwestern Memorial Hospital in "grave condition" and was declared dead there, Police News Affairs Officer Robert Perez said.

Police conducted an honor motorcade between Northwestern Memorial and the Cook County medical examiner's office this afternoon, police said.

Ross' aunt, Jackie Ross of Riverdale, said her nephew seemed happy when she spoke to him last month and she did not know of him suffering any health issues.

Ross described Preston Ross Jr. as a kind, outgoing and generous person who loved to barbecue.

"I've never seen him do anything in anger," said Ross, who has been married to Preston Ross’ uncle for 34 years. "I’ve never seen him angry, period. I’ve never seen him frown on anybody."

Ross added that whenever a family member or friend had a problem, Ross Jr. could be counted on to help out.

"He was a very sweet person," Ross said. "I was proud to say he was my nephew."